Arrangement for anchoring a floating body

ABSTRACT

A floating body is anchored by plural anchor chains having means for limiting the tension therein. Each chain runs through an eye of the anchor to a completely and permanently submerged float so that when a predetermined maximum tension is reached, the chain is drawn through the eye and the float sinks further in the water. A stop on the chain between the anchor and the anchored body limits the height to which the submerged float can rise in the water.

limited @tats atent Van Heijst ARRANGEMENT FOR ANCHORHNG A FLOATING BODY Willem Jan Van Heijst, Monte Carlo, Monaco Assignee: N.V. lntlustrieele lhlandelscombinatie Holland, Rotterdam, Netherlands Filed: June 11, 1973 Appl. No.: 368,889

inventor:

Foreign Application Priority Data June 12, 1972 Netherlands 7208003 US. Cl. 114/206 R, 9/8 P, 114/230 int. Cl. B63b 21/46 Field of Search 114/206 R, 230; 9/9, 8 R,

References Cited UNITED STATES PATENTS Ellingson 9/9 1 Feb. 111, 1975 2,478,217 8/1949 Walters et a1 114/230 2,986,888 6/1961 Borrmann et a1 114/206 R 3,111,926 11/1963 Shatto 4. 114/206 R 3,151,594 10/1964 Collipp 114/206 R FOREIGN PATENTS OR APPLlCATIONS 493,138 l/192l France 114/230 Primary Examiner-Trygve M. Blix Assistant Examiner-Galen L. Barefoot Attorney, Agent, or FirmYoung & Thompson [57] ABSTRACT A floating body is anchored by plural anchor chains having means for limiting the tension therein. Each chain runs through an eye of the anchor to a completely and permanently submerged float so that when a predetermined maximum tension is reached, the chain is drawn through the eye and the float sinks further in the water. A stop on the chain between the anchor and the anchored body limits the height to which the submerged float can rise in the water.

3 Claims, 3 Drawing Figures ARRANGEMENT IFOR ANCHOIRHNG A FLOATING BODY The invention relates to an arrangement for anchoring a floating body and which comprises two or more anchor chains extending therebelow and anchored in or to the sea-bed. Such an anchoring arrangement is generally known, and an example thereof is a ship moored fore and aft by anchors or a buoy having a number of anchors set out therearound. If one wants to maintain the floating body in a more accurate position the anchor chains can be initially tensioned accordingly. The elasticity of the anchoring arrangement and the movability of the floating body therethrough is dependent on the weight and the form of the anchor chain or chains, which movability is decreased with the tightening of a chain or chains. Too great a tightening in a chain or chains results in breakage thereof.

For buoys and floating islands, it is of the greatest importance that they should be anchored accurately in their places of operation in consideration of respectively, the lines connected thereto, or the work which is to be executed therefrom such as offshore drilling whilst, on the other hand, under no circumstance must the anchor chains break.

The present invention aims at providing a simple solution to this problem, and this aim is achieved according to the present invention in that a number or all of the chains are each fed through a guide-member of the anchor particular thereto, and past the guide member coupled to a permanently and completely submerged float, each of which chains being provided with a stop thereon on the side thereof adjacent the body to be anchored, and each of which stops cannot pass the guidemember. Through this measure, and by the correct choice of float, it is possible for the chains to be pulled through the guide-member when a certain tension in the chain, below the breaking-strain, is reached and whereby the float is pulled deeper into the water, and such that a more constant tension in the chain results. Should then the initial tension in one, or more, of the chains be exceeded the float(s) then exercise their function such that the tension in the concerned. chain, or chains, is maintained constant. The tension in a chain at which the float particular thereto exercises its function can be higher than the initial tension, but it must also be below the limit at which the danger of breakage of the chain begins.

It is known to anchor a ship by a cable which is coupled, via a return sheave on the sea-bed, to a float at sea-level, which float constantly functions to exercise a varying anchoring force which is dependent on the degree to which the float is submerged. This system is disadvantageous, in particular when movement of the ship and float are out of phase since then suddenly large forces manifest themselves in the cable.

The present invention will be understood from the following description read with reference to the accompanying drawings in which:

FIG. 1 schematically illustrates an anchoring arrangement according to the invention, and

FIGS. 2 and 3 are force/displacement diagrams.

Referring in the first instance to FIG. 1, a mooring buoy l is provided with a turn-table la for the mooring thereto of a tanker, or ship (now shown). The buoy l is anchored to the sea-bed with the aid of anchor chains 2. Only two chains are illustrated in the drawings alrangement the anchor chains extend to anchors in the form of, for example, concrete blocks. In FIG. I anchores 3 are shown which extend into the sea-bed al- 7 though any type of anchor is employable with the provision that it is equipped with a guide-eye 4 through which an anchor chain 2 can run. Each of the chains 2 is provided with a stop 5 thereon, and with the portion 2 a thereof, passed through the guide-eye 4, coupled to a float 6 which is in a submerged condition.

The chains 2 hang with a certain initial tension therein. Should the chains be displaced to assume the positions illustrated by the chain-dotted lines, then the most heavily loaded one thereof will, on reaching a certain predetermined tension therein, exert a pull on the float particular thereto such that the tension in the chain will not increase.

FIG. 2 shows a diagram in which the displacement of a fore-and-aft anchored body is indicated along the horizontal axis of the graph and in which the corresponding anchoring forces are indicated along the vertical axis threof. The relationship between displacement and corresponding anchoring forces is given by the curve 10.

If a ship is subjected to a force PI then its displacement will be from O to AI, and the energy taken up in anchoring is indicated by the hatched area 11.

As the result of the attendant and changing forces the ship will be displaced to and fro between, for example, points A2 and A3; and such that, in principle, the energy taken up is equal to the energy expended (represented by the hatched areas 12 and 13 of FIG. 2).

Should a pull on a chain, corresponding to the anchoring force P2, become too high then the pull in the chain will be limited by the pulling of the float downward thereby.

In principle, the diagram of FIG. 3 is the same as the diagram of FIG. 2. It illustrates however, what occurs when the predetermined limit of tension in a chain is reached through the application of the force P3, when the float is activated to perform its function. The force P3 then remains constant over the whole range of permitted displacement of the float 6..

As clearly shown in the diagram, it has been found that the energy which can now be taken up is considerably greater and such that the anchoring arrangement can stand heavier anchoring conditions, and higher initial tensions can be applied to the same chains.

What we claim is:

I. An arrangement for anchoring a floating body, comprising a plurality of anchor chains secured to and extending below the floating body, a plurality of anchors on the sea bed, each anchor having a guide member through which a said anchor chain slidably extends, a permanently and completely submerged float on the end of each anchor chain remote from the floating body, each said chain having a stop thereon between the floating body and the anchor which stop is closer to the associated said float than to said floating body so as to maintain said float permanently and completely submerged and said stop cannot pass through said guide member, the distance between each stop and its associated said floating body being; such that the floating body remains floating on the surface of the water when any said stop engages its associated said anchor, the length of said anchor chain between each said stop 3 4 and said floating body being substantially greater than said anchor. the vertical distance between any said anchor and said 3 An arrangement as claimed in claim 2, the lengths floating body.

2. An arrangement as claimed in claim 1, the length of each said anchor chain being such that when any 5 said float contacts its associated said anchor, a said stop from its Said associated anchorof another said anchor chain will contact its associated of said chains being such that said another anchor chain lies slack on the sea bed to a substantial distance 

1. An arrangement for anchoring a floating body, comprising a plurality of anchor chains secured to and extending below the floating body, a plurality of anchors on the sea bed, each anchor having a guide member through which a said anchor chain slidably extends, a permanently and completely submerged float on the end of each anchor chain remote from the floating body, each said chain having a stop thereon between the floating body and the anchor which stop is closer to the associated said float than to said floating body so as to maintain said float permanently and completely submerged and said stop cannot pass through said guide member, the distance between each stop and its associated said floating body being such that the floating body remains floating on the surface of the water when any said stop engages its associated said anchor, the length of said anchor chain between each said stop and said floating body being substantially greater than the vertical distance between any said anchor and sAid floating body.
 2. An arrangement as claimed in claim 1, the length of each said anchor chain being such that when any said float contacts its associated said anchor, a said stop of another said anchor chain will contact its associated said anchor.
 3. An arrangement as claimed in claim 2, the lengths of said chains being such that said another anchor chain lies slack on the sea bed to a substantial distance from its said associated anchor. 